| As a kind of ferrite material with specially physical and chemicalproperty, cobalt ferrite plays an important role among the magnetic materials. Cobaltferrite is extensively applied in magnetic recording materials, absorbing materialsand biomedicine because of its high coercivity, attractive value of high frequencymagnetic conductance and large magneto crystalline anisotropy constant, stablechemical properties, and corrosion resistance. Recently, control of structure andmagnetic properties of CoFe2O4has been an important researching orientation. Thispaper firstly studies the influence of conditions of sol gel method on the structureand magnetic properties of CoFe2O4, and the best condition is firmed. Then, on thebase of the prior researching, sol gel is used to study the influence of rare ionsdoping on the structure and magnetic properties of CoFe2O4. At last, CoFe2O4nanowires are synthesized by hard template method, and it realizes control of thestructure and magnetic properties by control of the morphology of CoFe2O4.In this paper, CoFe2O4nanopowders are synthesized by sol gel method. Then,influence of the ratio of metal ions to the content of citric acid, pH value, sinteringtemperature and sintering time on the structure and magnetic properties is discussed.The results from XRD and FESEM indicate that the samples show single spinelphase when the pH≦7and the sintering temperature is above450℃, and with theincrease of sintering temperature the crystalline size of CoFe2O4increase accordinglyfrom20nm to90nm. The results from VSM show that the best preparationconditions of pure CoFe2O4nanocrystalline synthesized by sol gel method are thatratio of citric acid and metal ions is2:1, pH value of the reaction solution is3,sintering temperature is800℃and the sintering time is3h. CoFe2O4prepared underthis condition has a crystalline size of66.8nm, a coercivity of1152.3Oe and asaturation magnetization of80.29emu g-1.Rare ions are usually used to adjust the magnetic properties of ferrite because oftheir large magnetocrystalline anisotropy energy. In this paper, influence of rare ions on the structure and magnetic properties of CoFe2xRExO4(RE=La、Pr、Sm、Gd、Dy; x=0、0.025、0.05、0.075、0.1) is systematacially studied. The change of magneticproperties is explained by super exchange action theory and the single particleanisotropic theory model. Study of crystalline size shows that the existence of rare ionsmakes the size of CoFe2O4smaller. The result of VSM shows that at roomtemperature, dilution effect of rare ions on magnetic moment makes decrease ofsaturation magnetization of CoFe2O4with the increase of content of rare ions. As theeffect of crystalline size, magnetocrystalline anisotropy and superexchange, rare ionsdoping less than0.025can increase the coercivity of the samples, but it decreaseswith the increase of rare ions content. This reaches the purpose to control themagnetic of CoFe2O4.SBA15mesoporous materials have specialities of tunable pore size and easy toremove template. In this paper, the pore size of SBA15is adjusted by controllingthe hydrothermal temperature, and then the SBA15is used for hard template ofCoFe2O4nanowires. Self assembly method is used for synthesis of CoFe2O4nanowires of different diameters, and the magnetic properties are tested. The resultshows that the pore sizes of SBA15mesoporous templates increase with theincrease of hydrothermal temperature, leading to the increase of diameter of CoFe2O4nanowires. Among them, nanowires with the diameter of9nm have a regular arrayaccording to SBA15. All the CoFe2O4nanowires have magnetic properties offerrimagnetism. Saturation magnetizations of nanowires with the diameter of6nmand13nm are60.39emu g-1and57.09emu g-1, which are lower than that ofnanowires with diameter of9nm. This is because of the dilution effect of Fe2O3. |
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